The present invention relates to a mold for a continuous-casting process. More particularly this invention concerns such a mold provided with an electromagnetic mixer.
In the continuous casting of metal an upwardly and downwardly open tubular mold is used into which the liquid metal is poured. The walls or sides of the mold are cooled so that the metal solidifies in this mold at least in an outer skin before it withdraws from the lower end of the mold. The interior of the workpiece in the mold at least is still liquid and forms a so-called crater. The sides of the mold are normally made of highly conductive material such as copper in order to maximize heat exchange between the casting being continuously formed and the mold which itself is normally cooled by means of water.
The main problem in continuous-casting operations is that due to thermal contraction the skin of the casting separates from the mold so that the rate of heat extraction from the casting is relatively low. Furthermore, the casting produced by this method often is inadequately homogenous so that it cannot be used for the production of many types of metals, in particular steel.
It has been found possible to partly solve some of these problems by providing on at least one of the sides of the mold a heavy-duty inductor whose magnetic field passes through the casting and produces eddy currents that serve to mix the molten metal in the casting, thereby increasing homogeneity of the casting so produced and also augmenting heat exchange. Thus it is possible to produce a high-quality bloom, slab, or billet even with steels that have hitherto often been considered unsuitable for continuous casting.
A principal difficulty with such arrangements is that the mold is not sufficiently rigid. Thus, the casting produced by the mold is often relatively irregular so that its subsequent rolling becomes rather difficult. The provision of coils in the cooling box adjacent the long sides of the mold further greatly reduces the rigidity of most mold structures so that it is necessary to make a trade-off between supporting structure and inductive capacity. For this reason the coil is often inadequately small in order to allow various braces to be mounted inside the cooling box. In particular when the ferrostatic pressure of casting and the hydraulic pressure of the coolant is relatively high it is necessary to provide so very many supporting structures inside the cooling box that only very small inductors can be fitted in. A solution to this has been attempted by increasing the depth of the cooling chamber. Thus, the number of ampere-turns is increased, but nonetheless it becomes very difficult to rigidify the cool side of the mold across such a deep cooling box. This also makes the installation relatively bulky and quite heavy.